This invention relates to new anode materials for lithium ion batteries. More specifically this invention relates to new anode materials for lithium-ion batteries consisting of intermetallic materials having active and inactive metals with respect to lithium, such as for instance Sn and Cu metals, respectively. Lithium-ion batteries are under development for the consumer electronics market such as cellular phones, laptop computers, and camcorders. Lithium batteries are also being developed for high energy/power systems such as electric vehicles. A major concern about lithium batteries is safety, primarily when metallic lithium is used as the anode material. This arises because lithium has a very high oxidation potential and thus reactivity in the cell environment. One approach to the safety issue is to use carbon as a host structure for lithium. The carbon can be either graphite or a less crystalline form of pyrolyzed carbon. Lithium-intercalated graphite/carbon electrodes improve the safety of lithium cells, but do not completely overcome the safety problems, because there is still the possibility of depositing metallic lithium at the top of the charge when the voltage of the lithiated carbon/graphite anode approaches that of metallic lithium. Carbon itself when present in a finely divided form with a high surface area, can be highly reactive particularly if oxygen is released within the cell from a highly oxidizing cathode material such as Li1xe2x88x92xCoO2, Li1xe2x88x92xNiO2, and Li1xe2x88x92xMn2O4.
There is, therefore, a need to find alternative anode materials to carbon. Many binary lithium alloy systems, such as LixAl, LixSi and LixSn have been extensively studied in the past. These alloys undergo several phase transitions during charge and discharge; the structures undergo severe lattice expansion and contraction that limits the cycle-life of the electrode. An improvement in cycle-life has been made by using an amorphous tin oxide negative (anode) electrode, in which the tin ions are initially reduced to a metallic state (during the charge process of lithium-ion cells), and thereafter alloyed with lithium to form a series of phases within the LixSn system (0 less than xxe2x89xa64.4). Several high-temperature phases are known, in order of increasing lithium content, they are: Li2Sn5, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2 and Li22Sn5; they are generated during the electrochemical reaction of lithium with tin at 400xc2x0 C. At 25xc2x0 C., the electrochemical profile has indicated that the compositions of the stable phases are Li2Sn5, Li2Sn3, Li7Sn3, Li5Sn2, Li7Sn2 and Li22Sn5. Tin-oxide electrodes suffer an irreversible capasity loss on the first cycle because a significant amount of the lithium is trapped within the charged electrode as lithium oxide. Furthermore, lithium oxide is an insulator, which reduces the electronic conductivity of the electrode, a serious disadvantage since for optimum performance the anode needs to be an electrical conductor.
We have invented a new anode for a lithium battery by replacing the oxygen of a tin oxide electrode with a metal such as copper, which has not only excellent electrical properties, but also has a low oxidation potential, and therefore a low reactivity in a lithium cell environment; copper foil is also used as the current collector at the negative electrode in conventional LixC6/Li1xe2x88x92xCoO2 lithium-ion cells. More generally, the invention relates to the use of intermetallic compounds, based on the structure types of copper-tin and lithium-copper-tin materials, as defined by their relationship to NiAs type, Ni2In type and lithiated zinc-blende-type materials as anode materials for rechargeable lithium batteries. The invention also includes nonaqueous electrochemical cells incorporating the new anodes and the methods of making the anodes and cells. In the anode, there is one or more of an active metal which can alloy substantially with lithium (such as tin) and, in most instances, there is one or more of an inactive metal which does not substantially alloy with lithium (such as copper). There are other examples in which the anode material components consist of two (or more) active metals that can alloy with lithium, such as tin and germanium.
The invention also includes cells and batteries incorporating the new anode materials with standard state-of-the-art cathodes such as lithium cobalt oxide, lithium nickel oxide or lithium manganese oxides (and various substituted oxides), cathodes now useful in lithium rechargeable batteries.